1. Introduction to Reaction Rates
Introduction & Methods of Initial Rates

2. Collision Theory
In order for reactions to occur, 3 things must happen:
Atoms or molecules must ___________
The must collide with the proper ___________
The must collide with sufficient ___________

3. Chemical Kinetics
___________ - area of chemistry that is concerned with reaction rates and reaction mechanisms
The rate of a reaction depends on the collision ___________ of the reactants and on the collision ___________.

4. Factors that Affect Reaction Rates
Nature of the ___________
___________ of the reactants
___________

5. Activation Energy
___________ - the minimum amount of energy that particles must collide with to make a reaction occur

6. Activation Energy & Catalyst

7. Intro to Reaction Rates
____________ – how fast the reaction takes place
The rate is usually measures in Ms-1

8. Graphing the reaction progress
For the reaction
2NO2  2NO + O2
Graph what happens to the concentrations of the reactants & products as the reaction progresses

9. Graphing the reaction progress
Concentration
(M)
Time (s)

10. Rate Law Types Differential Rate Law Integrated Rate Law
Usually just called the rate law
Comes from calculus (derivative)
Finding the slope of the curve
Slope rate
Integrated Rate Law
From integrals

11. Form of the Rate Law Differential Rate Law Rate = k[A]x[B]y
Rate = Ms-1
K = rate constant – found only experimentally

12. Determining the Order of the Rate Law
Rate = k[A] 1st order
Rate = k[A]2 2nd order
Rate = k[A][B] 2nd order
Rate = k[A]2[B] 3rd order
Rate = k[A][B]2 3rd order
To get the reaction order, you just add up all of the exponents

13. Units of k Units of rate are usually Ms-1
Can get units of k from the formula for the rate law
1st order
K = s-1
2nd order
K = M-1s-1
3rd order
K = M-2s-1

14. Integrated Rate Law Zero order 1st order 2nd order Rate = k
ln[A] = -kt + ln[Ao]
2nd order
1/A = kt = 1/[Ao]

15. Method of Initial Rates
Choose 2 experiments in which all but 1 variable changes when divided
Rate1 = k[A]x[B]y
Rate 2 k[A]x[B]y
Cancel out all but 1 of the exponents to solve for x or y
Solve for the other (x or y)
Use one experiment to solve for k
Find units for k

16. Example
What is the rate law?
What is the value for k including units?

17. Example 2 S2O8-2 + 3I-  2SO4 -2 + I3- determine the rate law
Determine the value of the rate constant
How is the rate of the disappearance of S2O8-2 related to the disappearance of I-?
What is the rate when [S2O8-2] = 0.015M & [I-] = 0.040m?
Experiment
[S2O8-2]
[I-]
Rate 1
0.018
0.036
2.6 x10-6 2
0.027
3.9 x10-6 3
0.054
7.4 x10-6 4
0.050
0.072
1.4 x10-5

18. Graphs and kinetic data
a straight-line graph shows zero order w.r.t that reactant.

19. Graphs and kinetic data
a constant half-life graph shows first order w.r.t that reactant.

20. Plotting initial rates against concentrations of the reactants.
Zero order – rate is independent of concentration

21. Plotting initial rates against concentrations of the reactants
First order reaction – rate is directly proportional to concentration

22. Plotting initial rates against concentrations of the reactants
Second order reaction - varies